(1) Field of the Invention
The present invention relates to a plastic laminate structure. More particularly, the present invention relates to a plastic laminate structure comprising an ethylene terephthalate type or butylene terephthalate type polyester layer and a gas barrier layer of an olefin-vinyl alcohol copolymer, both the layers being tightly bonded together through an ester-amide type adhesive layer. Especially, the present invention relates to a plastic laminate structure which is excellent in the combination of the gas barrier property, rigidity, interlaminar peel strength and transparency and is valuably used for the production of a sealed storage vessel.
(2) Description of the Prior Art
Since polyethylene terephthalate is excellent in the moldability and can be molecularly oriented biaxially, it is widely used for the production of light-weight plastic vessels excellent in the impact resistance, rigidity, gas barrier property, light weight and transparency, especially bottles for drinks. However, the gas permeability of this polyester bottle is significantly higher than that of a glass bottle, and it is said that the shelf-life of the polyester bottle is about three months when it is filled with a carbonated drink such as cola.
An olefin-vinyl alcohol copolymer such as a saponified ethylene-vinyl acetate copolymer is known as a thermoformable resin excellent in the oxygen barrier property. Furthermore, it is known that this resin can be used in combination with an olefin resin excellent in the moisture resistance for the production of an undrawn or drawn multi-layer plastic vessel.
Proposals have been made as to vessels composed of a laminate of a polyester and an olefin-vinyl alcohol copolymer, and it is naturally expected that this laminate will be excellent in the combination of the gas barrier property, impact resistance and rigidity. However, this laminate has not practically been used for the production of a vessel, especially a biaxially drawn blow-molded vessel. The reason is considered to be that a thermoplastic adhesive capable of forming a strong interlaminar bonding between the polyester and olefin-vinyl alcohol copolymer has not been found out.